With such an apparatus currently used, a print format has been switched from transaction printing to POD (Print on Demand) printing. The transaction printing performs typical printing onto continuous-form paper. The POD printing often performs various types of printing depending on a print medium such as exclusive paper for inkjet or coated paper. The POD printing requires printing with higher accuracy.
Examples of the apparatus performing high-accurate printing include the following. For instance, a first apparatus (see, for example, Japanese Patent No. 4518584A) and a second apparatus (see, for example, Japanese Unexamined Patent Publication No. H06-70112A) have been suggested. Specifically, the first apparatus has devised arrangement of rollers on a transport path so as to obtain an accurately maintained gap between a printing unit and a printing surface of a printing sheet. The second apparatus has devised an encoder so as to be disposed closed to a printing unit for accurate detection of a transportation speed of a printing sheet.
However, the examples of the currently-used apparatus with the above configurations have the following drawback.
Specifically, the currently-used first apparatus achieves the accurately maintained gap between the printing unit and the printing surface of the printing sheet. This allows enhanced printing accuracy. Moreover, the currently-used second apparatus achieves the accurate detection of the transportation speed of the printing sheet. This also allows enhanced printing accuracy in the transportation direction. However, such the apparatus may produce a drawback that paper flotation or unevenness by wind may cause reduction in printing accuracy. The paper flotation occurs by floating-up of the printing sheet from the transport path by a variation in transportation direction. The unevenness by wind occurs as under. That is, the transportation of the printing sheet causes air flow into the gap between the printing unit and the printing surface of the printing sheet. This leads to the unevenness by wind of disturbing discharge of ink droplets.